Construction and control of planetary mills



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United States Patent O Tadeusz Sendzimir, T. Sendzimir Inc., Oxford Circle, Waterbury 12, Conn. Filed July 29, 1959, Ser. No. 830,216 22 Claims. (Cl. 80--38) This invention relates` to planetary rolling mills such as are described in United States Patents 2,710,550 and 2,811,060 and in the copending United States application Serial No. 436,075 of applicant, now Patent No. 2,962,951 tiled lune 11, 1954, and entitled Dual Drive Planetary Reducing Mills, and also to mills such as those described in British Patent 609,706 to E. Picken, i.e. to mills of the type in which successive pairs of working rolls, one on each side, pass progressively across a zone of plastic deformation of a work piece While in rolling. contact therewith. The working rolls are arranged in planetary assemblies about each of a pair of backing rolls or their equivalent. The direction of translation of the working rolls while in contact with the work piece is usually from the unreduced portion toward the reduced portion of the work piece; and while each pair of working rolls may make a reduction in the zone of deformation comparable to that produced in a single pass in a conventional mill where the working rolls rotate around a fixed axis, and where reductions of between and 35% in a hot rolling operation are exemplary, in the planetary mills of the type here under discussion, by reason of the fact that there are many pairs of working rolls which pass in a rapid succession past each portion of the work piece in the zone of deformation, the total reduction is usually many times more than that on any conventional mill. A planetary mill acting to reduce a steel slab 40 in. wide and 31/2 in. thick to strip metal having a 40 in. Width and a thickness of about 0.100 in. is exemplary but not limiting. The reduction just set forth is a 97% reduction and produces an extension of the metal to 35 times its original length.

The teachings of this application are directed primarily to the correction of difliculties which have been found to arise during the actual operation of the mill on a work piece or series of work pieces. It has been found that during the rolling of slabs certain operational characteristics tend to arise which interfere with the proper reduction of the work piece, and with the operation of the mill as a mechanical unit and which in some instances result in serious mechanical damage to the mill, including broken gear teeth, twisted shafts, damaged keyways and the like. These diiculties have now been traced to inequalities in the operation of the working rolls, which inequalities are conveniently indicated by the term synchronization using that terrn in a generic sense. Means have hitherto been provided in mills of the type to which this invention is addressed for causing the opposite ones of the working rolls to contact the work piece simultaneously, which is an aspect of synchronization; but it has been found that if something occurs to disturb the proper coaction of the rolls during a rolling operation, the apparatus heretofore provided for causing opposite working rolls to contact the work piecesimultaneously and which generally comprises gears, shafts, couplings and power units is subject to shock load which is sometimes unpredictably high. It has been found further that once a planetary mill develops a condition in which the working rolls depart from proper coaction further operation of the mill usually increases the degree of asynchronization. The greater the departure of the working rolls in the zone of plastic deformation from proper coaction, the

. ICC` greater will be the force needed to prevent further departure from proper coaction. VIt has not been found possible to cure these defects by making the hitherto known synchronizing means extremely heavy and rigid.

There are forces in the planetary mill which tend to interfere with proper coaction of the working rolls in the zone of plastic deformation despite extreme rigidity in the means hitherto provided for synchronization. These forces arise during rolling for various reasons including, among others, changes occurring as a result of wear, local expansion due to heat, inequalities in the ilow of lubricant, and inequalities in the work piece. Work pieces may not only vary in physical shape in different parts, but they also may vary in temperature sporadically, and from side to side. There vis almost always a temperaturel variation in the direction of the length of the work piece, the trailing end of a Work piece being commonly at a lower temperature than the leading end of the same, or a successive work piece. For example, a mill with newly reground rolls and checked for synchronism may operate perfectly for half a day and then gradually develop a tendency such that the irst end of each strip points sharply downwards (or upwards) instead of horizontally, even to the point of getting under the stripper and causing a loop, and in consequence, a cobble. This is usually accompanied by a shifting of the slab vertically, in the zone of'deformation, away from the roll assembly that is in advance.

This condition in turn causes the angle of incidence of the lower working rolls against the slab to become greater which may lead to development of backins (such as described in U.S. Patent 2,710,550). In their incipient stage, such backins are small discontinuous rolled-in slivers and are very detrimental to the surface quality of the finished strip.

When continuing operation under these conditions the operator must be on the alert because the situation may aggravate itself in a matter of a few seconds, and unless the mill is not suddenly stopped, serious damage is caused.

The term synchronization as used herein is intended to be inclusive of the matter of parallel alignment of the axes of the working rolls with the axes of the backing rolls. If this alignment is departed from, the working rolls come out of parallelism and are skewed The consequence is usually a lateral translation of the slab in the working zone; and this occurs sometimes with such great force that`no lateral guide is capable of holding it.

Defects in synchronization are also likely to occur due to the action of screwdown means when adjustments are made to change the iinal gauge ofthe material being rolled; and this brings up another difculty which could be termed a departure from symmetry, but for purposes of this application will be considered under the heading of synchronization because it affects synchronization. Where the upper backing roll is shifted vertically, as by means of conventional screwdowns, in order to change or adjust the gauge, the result is a shifting of the zone of plastic deformation above or below the plane of symmetry of the mill. Rolling is most eilicient when the plane of symmetry of the zone of plastic deformation lies midway between the paths of operation of the two sets of planetary working rolls. A shifting of the plane of symmetry toward or away from either planetary assembly produces, in itself, the effect of lack of synchronization of the working rolls.

While an experienced planetary mill operator is frequently able to note changes in the behavior of the mill in time to stop it before serious damage is done, in the past there has been no way of correcting any of the difficulties hereinabove mentioned excepting by resetting ala-amo the mill elements which causes an interruption during which the mill cools down and the thermal equilibrium that affects synchronization is again upset.

Applicant has found that by carefully observing the position of the slab both in the vertical and lateral directions at the entry into the zone of deformation, and any tendency on the part of the slab to change its position, he could successfully anticipate the stepping of the rolls out of synchronism and cause the slab to return to its position in symmetry with the mill by adjustingy the synchronizing elements in a direction opposite to the direction of such shifting. The development of this new method of operating the planetary mill has permitted to roll without interruption and practically eliminate the danger of mechanical wrecks. It is, therefore, an object of this invention to provide means for such adjustment. The means herein taught may be controlled by an operator who is sensitive to any malfunction of the mill; but they also may be controlled by automatic mechanism.

It is thus an object of the invention to provide means whereby the simultaneous contacting of the work piece by opposite members of a pair of working rolls can be maintained by making appropriate adjustments during a rolling operation.

It is an object of the invention to provide a means whereby any skewing of the rolls may be controlled or corrected during a rolling operation.

It is an object of the invention to provide a means whereby the plane of symmetry of the zone of plastic deformation can be adjusted with respect to the plane of symmetry of the mill during a rolling operation.

In speaking of these corrections and adjustments, it should be kept in mind that there are circumstances in which a controlled degree of asynchronization, a controlled degree of skewing, or a controlled departure of the plane of symmetry of the work piece from the plane of symmetry of the mill may be desirable to overcome certain specific conditions, usually conditions of inequality in the work piece itself; and that the term control as herein used is intended to be broad enough to cover the attainment of predetermined degrees of any of the aspects of asynchronization for specific purposes.

The attainment of the principal objects of the invention provides a number of ancillary advantages which also constitute objects of the invention, these, which will be set forth hereinafter or will be apparent to one skilled in the art upon reading these specifications, are accomplished by that construction and arrangement of parts and in that procedure of which certain exemplary embodiments will now be described. Reference is made to the accompanying drawings wherein:

FIG. 1 is a diagrammatic vertical section of a planetary mill with a pusher type feeder and showing a screwdown arrangement as applied to each of the planetary assemblies of the mill.

FIG. 2 is a diagrammatic vertical cross section of a mill showing a pair of feed rolls, a pair of planetary assemblies and pairs of pinch rolls located outside the mill housing.

FIG. 3 is a diagrammatic vertical cross section of a planetary mill including a pair of feed rolls, a pair of planetary assemblies, and a pair of planishing rolls, all included in the same housing. In this figure there is also illustrated a means for keeping a plurality of the working rolls of each planetary assembly in contact with the backing rolls on the sides opposite the zone of plastic deformation.

FIG. 4 is a longitudinal vertical section taken across the pair of planetary assemblies as shown in FIG. 3.

FIG. 4a is a partial vertical section showing a means for pre-loading the backing roll bearings.

FIG. 5 is a longitudinal vertical section taken through the plane of the finishing or planishing rolls of FIG. 3.

FIG. 6 is a diagrammatic longitudinal section through the pinions of an adjustable pinion stand coupled by d spindles to a planetary mill such as those shown in FIGS. l, 2 or 3.

FIG. 7 is an elevational view with parts omitted, of the pair of another type of planetary assemblies in which the main drive is applied to the backing rolls which in turn drive the Working roll cages, therefore, are freely revolving on the backing roll necks which arrangement requires synchronizing gears and means for their adjustment.

FIG. 8 is a fragmentary View showing a portion of a pair of planetary assemblies in vertical cross section together with an hydraulic screwdown control which is partially diagrammatic.

FIG. 8a is a diagrammatic showing of another portion of control means.

FIG. 9 is a partial vertical sectional view of a planetary assembly as shown in FIGS. 3, 4 and 8, showing the mounting of working rolls in their cages and their skewing adjustment and also showing a backing roll chock or bearing having screwdown features hereinafter described.

FIG. 10 is a diagrammatic View showing one means for the adjustment of the relative positions of cages or rings at the end of a backing roll of a planetary mill with directly driven backing rolls.

The various mechanical arrangements and constructions hereinafter described have both a combined and an individual utility; that is to say, they not only interact and coact to a given end, namely the control of all of the factors of asynchronization as described above, providing a mill which is eflicient in its operation and essentially not subject to destructive mechanical shocks, but they are also individually useful as such and useful in combinations containing less than the total number of elements herein described. The order in which the various novel mechanical elements going to make up this invention are described herein is not to be taken as the order of ltheir practical utility or importance. The endeavor has been to describe a mill or mills in a clear and understandable fashion from the standpoint of the functioning of all of the parts thereof.

Referring first to FIG. l, there is shown a planetary mill comprising a housing, part of which is shown at 1, `a pair of backing rolls 2 and 3 mounted in the housing, assemblies 4 and 5 of planetary working rolls each surrounding one of the backing rolls, and a slab 6 which is being reduced to a strip in the zone of plastic deformation of the mill. The slab 6 is being fed into the zone of plastic deformation by a pusher S on the piston rod 9* of a iiuid pressure cylinder 10 mounted on a suitable table Il. It is usual in thc operation of planetary mills of this type to roll the slab 6 in heated condition, but this constitutes no necessary limitation on the invention since the mill may be operated as a cold mill if desired.

The specific novelty illustrated in FIG. 1 is the provision of chocks or bearing elements for both of the backing rolls 2 and 3, which chocks also constitute adjustable screwdown means. The chocks are arcuate in peripheral contour and are mounted in circular recesses or perforations in the housing 1, while the necks of the backing rolls 2 and 3 are eccentrically mounted in the chocks. The chocks are indicated in the figure at 12 and 13 and means are provided for rotating the chocks in the housing which will have the effect of moving the axes of the rolls 2 and 3 simultaneously toward and away from each other. While eccentric chocks are known, applicants chocks are limited in their periphery to an arc of a circle which permits a rotation over about 60 only. At the same time their eccentricity is many times larger than known eccentric chocks permitting a full revolution.

While there are many ways in which the chocks may be rotated, a simple arrangement is shown in FIG. l in which the piston rod IA of a fluid pressure cylinder IS mounted on the upper end of the housing l is connected to the chocks I2 in an eccentric position. Similarly, the piston rod I6 of a fluid pressure cylinder 17 mounted on the lower end of the housing 1 is connected to the chock 13 in an eccentric position. lt will be evident that excitation of the iluid pressure cylinders will produce a limited rotative movement of the chocks 12 and 13, moving the axes of theA backing rolls 2 and 3 simultaneously toward and away from each other. If the two cylinders are actuated simultaneously, and equally in the same operative direction, the screwdown will be varied without changing the plane of symmetry of the mill. If the two cylinders are actuated simultaneously equally but in opposite operative directions, the screwdown of the mill will remain substantially the same but the plane of symmetry will be shifted. If the two cylinders are actuated differentially, the screwdown can be changed and the plane of symmetry simultaneously shifted.

During a rolling operation, the provision of a screwdown on both` of the backing rolls permits the operator (or automatic devices if desired) p to make minute adjustments quickly and precisely in the position of the plane of symmetry of the mill. The arrangement also has a number of other advantages. It is only necessary to move each screwdown a little more than half the thickness of the yslab to open the mill completely and release the slab as in the case of a cobble.Y Another advantage lies in the fact that the arrangement permits a considerable reduction in the size of the mill housing. ln planetary mills as hitherto constructed, the upper backing roll had its ends or necks mounted in rectangular checks or bearings slidable in slots in the housing. These bearings not only had to be quite large in themselves, but the provision of the slots (which had to be substantially longer than the entire required range of movement of the screwdown), and the provision of screw means threaded into the upper part of the housing, considerablyweakened the housing itself. Hence it was found necessary to use housings which were quite large as compared with the working parts of theV mill. But in a structure such as that shown in FIG. l, since the roll separating force is transmitted by the chock to the housing on a large curved area, the housing is subjected, in much the same way as a loaded pressure vessel, to tensional stresses primarily and to practically no bending moments. This very greatly reduces the deflection of the housing under load; and it has been found that housings designed as in FIG. 1 can weigh less than half of the necessary weight of former housings while possessing a rigidity 2 or 3 times greater. It becomes possible, moreover, even on fairly large sized mills such as those rolling strips 50 in. or more in width, to produce a complete mill'housing including both end housing members and connecting beams such as those shown at 18, 19, 20 and 21 in FIG. l as a single casting. This adds substantially tothe over-all rigidity and lateral stability of the mill. In a conventional type of mill of the same size, each end housing member would by itself weigh over 300,00() lbs. which would make any combination of the two in a single casting impracticable.

It will be understood that in many mills guides will be provided to conduct the slab to a point as close as possible to the zone of engagement of the Working rolls with the work piece. These guides have not been illustrated in the drawings. It will be understood that where guides are used it will be within the scope of this invention to provide for adjustments of their positions transversely of the zone of plastic deformation.

In some mills feeding is accomplished by feed rolls, and it is advantageous to locate such rolls as close as possible to the planetary assemblies to reduce the tendency to buckle and to shorten the time interval from furnace to plastic reduction. The pinch rolls may be located in the same housing as the planetary assemblies. This is illustrated in FIG. 2 where like index numerals have been used to indicate like parts. A pair of driven feed rolls 22 and 23 are shown as mounted eccentrically in chocks 24 and 25 which in turn are rotatably mounted in the housing 1. These chocks act in the same way as the checks 12 and 13 previously described, and may be controlled in the same way as by hydraulic cylinders 26 and 27, the piston rods of which are connected to the chocks. A considerable force is generally required to feed slabs into the planetary mill, as a consequence of which it is usually necessary for the feed rolls 22 and 23 to bite into the slab, i.e. to take a small reduction in it. The mounting and adjustment means for the feed rolls just described not only act as a screwdown to regulate the bite of the feed rolls on the slab, but it will be evident that if the cylinders 26 and 27 are operated in a differential fashion, the feed rolls may be employed to raise or lower the plane of symmetry of the slab to make it conform at the feeding point to the plane of symmetry of the reduction zone between the planetary assemblies. The feed rolls 22 and 23 will be driven by suitable means.

It may be noted that an independent adjustment of the feed rolls as described, particularly in varying the position of the plane of symmetry of the slab is often suflicient to correct a malfunction of the mill without adjustment of the planetary assemblies, although both the feed rolls and the planetary assemblies may be adjusted concurrently or sequentially if desired.

It has further been found that if independent drives are provided for the feed rolls 22 and 23, a slight disparity in the speed of operation of the feed rolls will have the effect of causing the emerging slab to move slightly toward the feed roll which is being driven at the slower speed. This also provides a feature of control which varies the tendency of the planetary mill to depart from perfect synchronism.

In a normal operation, the slabs will be fed sequentially from a continuous furnace located ahead of the mill. Such a furnace may employ high frequency electric induction heating, but other modes of heating are available. In a continuous operation of the mill the leading end of a succeeding slab will be used to push the training end of a leading slab through the mill. In FIG. 2 there have been shown means for feeding the slabs in succession from the furnace to the feed rolls 22 and 23. These means comprise pinch rolls 28 and 29 which, in the embodiment shown are mounted in chocks on lever arms 30 and 31 attached to the mill housing. The lower assembly, associated with the pinch roll 29 may be held in position by adjustable thrust means 32 connected with a foundation member of the mill. The upper assembly may be controlled by one or more hydraulic cylinders 33 attached to the mill housing. The pinch rolls 28 and 29 will be driven in any suitable fashion.

It is advantageous to withdraw the strip 7 'from the planetary assembly under tension, which tension assists the feeding force exerted on the slab by the feed rolls 22 and 23. As illustrated in FIG. 2 means for this purpose may be directly associated with the mill. The means include pinch rolls 34 and 35 journalled in chocks on lever arms 36 and 37 pivoted to the mill housing. Again the lower assembly may be supported by adjustable means indicated at 3S, while the position of the upper assembly is controlled by one or more fluid pressure cylinders 39 attached to the mill housing. The pinch rolls 34 and 35 will be driven by suitable means not illustrated. It will be appreciated that the construction shown provides not only for regulation of the bite of pinch rolls 28, 29 and 34, 35 on the slab and strip respectively, but that the plane of symmetry of the slab and the strip is adjustable also. Fluid pressure control means may be substituted if desired for the mechanical adjustable devices 32 and 38. In operation, pinch rolls 28 and 29 assist substantially in assuring that the lirst end of a slab butts i.e., presses firmly against the last end of the preceding slab. It is evident that, as thelast end of a slab 6 passes through the bite of the feed rolls 22, 23, the following slab must be pushed into said bite with adequate force so as to cause the feed rolls to bite it too, otherwise a slight but very detrimental interruption in ansaevs the feeding function might occur. This initial pushing of the following slab is accomplished by the pinch rolls 28, 29 although other means can be used too.

FIG. 3 shows another embodiment of the invention in which feed rolls, planetary assemblies, and rolls on the exit side of the planetary assemblies are all mounted in the same housing. The exit rolls may be pinch rolls for tensioning purposes, or they may constitute a two-high planishing mill. Such a mill, in addition to tensioning, tempering, and ordinary surface functions may serve to iron out any transversely extending ripples or gauge inequalities produced by the operation of the planetary assemblies.

In FIG. 3 like numerals have again been used to indicate like parts. The rolls 4G and 4f. which may constitute the planishing mill are again advantageously mounted eccentrically in chocks 42 and 43 which are rotatable in the housing member i. The positions of the rolls 40 and d1 as respects each other may again be controlled by fluid pressure cylinders 44 and 45. The assembly of FIG. 3 not only provides in a single housing the combination of feeding rolls, planetary reducing instrumentalities and a planishing mill, but mounting these instrumentalities cccentrically in chucks rotatably in the housing provides for the use of a housing which is much smaller and lower in cost than conventional type housings designed to contain the same instrumentalities. Again it is usually possible to form the housing as a single casting with attendant advantages in rigidity and cost even in relatively larger mills. It is not beyond the scope of the invention, however, particularly for very large mills, to provide housings in the form of parts which must be bolted together.

Rigidity in a mill housing is important because of the fluctuating character' of the loads on the housing, inevitably caused by cyclic changes in the magnitude and direction of the roll separating forces depending upon the number of pairs of planetary working rolls in contact with the work piece at any given instant. The cycles occur usually between 20 and 80 times per second, and unless the housing is very rigid can give rise to detrimental vibrations and excessive noise. In comparison with conventional mill housings, the embodiment shown by applicant is not only much more rigid in the direction of the roll separating forces but is also very rigid in the direction of the feeding force. This is important since the feeding force is about 1/a as big as the rolling pressure and conventional housings with their long vertical columns have a rather poor rigidity in this direction. It is, of course, advantageous to be able to locate the feeding pinch rolls, the planetary assemblies and a tensioning device or planishing mill as close to each other as possible in the direction of motion of the work piece.

It will be evident from the foregoing description that the structure of FIG. 3 provides for adjustability of the plane of symmetry of the entering slab and the emerging strip to the plane of symmetry of the zone of reduction between the planetary assemblies.

It will be understood by the skilled worker in the art that the various chocks heretofore described as rotatably mounted in the mill housing may be rotated by various mechanical hydraulic or electrically driven means. Adjustment of any of these means may be wholly under the control of the mill operator; but adjustment may also be effected by automatically acting means.

Referring to FIGS. 8 and 8a, the hydraulic system operating the chocks may comprise a suitable electrohydraulic servo valve 46 connected to a hydraulic cylinder such as cylinder at points both above and below the piston 47 therein. The servo valve will be connected also with an electrically driven hydraulic pump 1S or other suitable source of fluid under pressure; it will also be connected with a sump or reservoir indicated at e9 in FIG. 8. The servo valve serves to maintain a predetermined hydraulic pressure difference on opposite sides of the piston 47, proportional to the value of an electric signal voltage fed to it. The magnitude of the hydraulic pressure difference which corresponds to the zero electric signal voltage may be mechanically pre-adjusted as is usually possible with electro-hydraulic servo valves.

A precision, linear potentiometer 50 may be mounted on the pressure cylinder 15 and connected to rod 51 which is an extension of the piston rod. Thus the potentiometer will follow exactly the movements of the piston. T he potentiometer Si) is represented in FIG. 8a at 50a, and it will be noted that it is connected to a reference potentiometer S2 in such fashion as to form a Wheatstone bridge energized by a source of current 53. The reference potentiometer 52 may be set manually by the operator. The imbalance of the resistances of the bridge caused by the movement of the runner of potentiometer 5) or 52, will produce a signal Voltage, amplified by an amplifier diagrammatically indicated at 54. This amplifier is shown as powered by a suitable source 55 of alternating current; and it is also shown as connected to the servo valve 46. Thus there will be produced on opposite sides of the piston 47 an hydraulic pressure difference which is proportional to the signal voltage and to the selected zero signal setting of the valve 46. The electric signal in the apparatus, caused by imbalance of the electric bridge, will be produced either by the adjustment of the reference potentiometer 52 by the operator or by the movement of piston 47 connected linearly with potentiometer 50.

Thus variations in the basic roll separating force (in the planetary assemblies for example) caused by the resistance of the rolled material to deformation, and proportional roughly to the kind. width, temperature and percentage reduction of the rolled material, will generate electric signals producing differences in the hydraulic pressures on each side of the piston 47 which will balance the said changes in roll separating force, Any variation of the basic roll separating forces which is large enough to overcome the inherent friction of the screwdown mechanism will produce a movement of the piston 47. If the operator wishes to change the roll distance either to increase or decrease the thickness of the rolled material, or to adjust the plane of symmetry, he can accomplish this by adjusting the reference potentiometer 52.

By suitable design of the mechanical parts and selection of the control components, the ratio of the variation of the roll separating force to the variation of the roll distance can be made so high that a substantial variation of the roll separating force will produce no change or only a negligible change in the position of piston 47, and hence in the thickness of the outgoing strip. On the other hand if accuracy in the thickness of the rolled strip is regarded as critical, means for measuring the strip thickness continuously, as known in the art, can be provided, and the correction of the gauge can be made either manually or automatically.

Automatic control of the strip thickness can be attained when known devices for continuously measuring strip thickness and of a type which generate an electric current are used, since it is possible to cause variations in the current so generated to effect a continuous adjustment of the reference potentiometer 52.

The servo valve 46 can be connected to a suitable source of electric current through a switch under the control of the operator so that if current from the said source is applied to the servo valve it will act as a solenoid operated four-way valve. This arrangement makes it possible for the operator to open the mill rapidly through the action of the hydraulic cylinder 15.

The control apparatus just described may be applied to the iiuid pressure cylinders of both planetary assemblies, to one or both of the fluid pressure cylinders of the feed rolls and to one or both of the rolls of an exit tensioning device or planishing mill.

Reference is made to FIGS. 4 and 5 which are longitudinal vertical sections of mills. In FIG. 4 the end mill housing element 1 is shown as containing the rotary chocks 12 and 13. The opposite end mill housing element is indicated at 1a and is shown as containing the chocks 12a and 13a. The end housing elements 1 and 1a are interconnected by the beams 18 and 19. Similarly the end mill housings 1 and 1a in FIG. 5 are shown as carrying the chocks 42, 43 and 42a, 43a respectively for the planishing rolls 40 and 41. Fluid pressure means for the several chocks are shown in FIG. 4 at 15, 17 and 15a, 17a and in FIG. 5 at 44, 45 and 44a, 45a. The checks may be held axially in place inthe respective housing elements by means of rings 56 or in other suitable ways. FIGS. 4 and 5 illustrate not only what is meant by a one piece housing as hereinabove set forth, but they also make it clear that since separate controlling means for the several chocks are provided on each side of the mill the screwdown effect may be adjusted transversely of the direction of rolling of the work piece. Thus if there is a discrepancy between the screwdown on one side and the screwdown on the other, this may be corrected; and it is also possible deliberately to adjust the screwdown on the one side of the mill so that the rolls exert a greater pressure on one edge of the slab or strip than the pressure exerted on the other to take care of specic inequalities in the strip existing in the lateral direction such as inequalities in gauge or temperature.

It has been indicated above that the working rolls have their end portions mounted in cages or rings. Where the working rolls are backed by solid, driven backing rolls (such as shown in FIG. 7) the rings are normally provided with gear teeth and are interconnected. Thus the ring ends, freely mounted for rotation on one of the backing rolls will be interconnected by a shaft bearing gears; and the rings of the other backing roll will be similarly interconnected, the shafts just mentioned passing transversely of the mill and being in line with the axes of the Working rolls. These shafts are interconnected at their ends by vertical shafts, the interconnection employing bevel gearing. In theory, one such vertical shaft would be suicient; but it is preferred to provide a vertical shaft at each side of a mill for the sake of added torsional rigidity.

Reference is made to FIG. 7 wherein the backing rolls 2 and 3 carry planetary assemblies 4 and 5. The ends of the working rolls are mounted in chocks in rings 57, 58, 59 and 60. These rings have portions provided with gear teeth as indicated. An upper transverse shaft 61 carries gear elements 62 and 63 which mesh with the gear teeth of rings 57 and 58. The necks of the working rolls are journalled in checks borne by the rings. As most clearly shown in FIG. 9 each such chock 64 has a spring mounting 65 with respect to its ring which urges the chock 64, and, therefore, also the working roll 5, toward the center of the backing shaft 112.

The gearing of the rings 57 and 58 together is intended to maintain the axes of the working rolls 4 in parallelism with the axis of the backing roll 2. In a similar fashion the rings 59 and 60 of the lower backing roll 3 are geared together by means of a transverse shaft 67 and gear elements 68 and 69. At the ends of the transverse shafts it will be seen that their Ybevel gears 70, 71, 72 and 73 mesh with bevel gears 74, 75, 76 and 77 on vertical shafts 78 and 79 at each side of the mill. A drive (not shown) either from the mill itself or from a separate prime mover may be applied to any of the shafts 61, 67, 78 and 79 to insure synchronous running before the work piece is engaged and for other known purposes,

- if desired.

The present invention contemplates adjustability of synchronization. One way of accomplishing this as to the vertical shafts is to divide these shafts into two parts. At the right hand side of FIG. 7 the shaft 79 is shown as divided into two parts designated 79 and 79a. These parts are provided with splines 80 and 81; and a positive drive between the two parts is eifected by a sleeve or coupling 82 having interior means engaging the splines. If either or both of the sets of splines 80 and 81 have a helical disposition in opposite directions, longitudinal movement of theV coupling 82 will effect a rotary adjustment between the shaft sections 79 and 79a. In order to permit the adjustment and fixing of the longitudinal position of the coupling 82 there is provided an element 83 threaded into a ixed bracket 84. The coupling 82 bears against the upper surface of the threaded element.

A similar arrangement may be made at the opposite s-ide of the mill for vertical shaft sections 78 and 78a. This similar arrangement is indicated generally by the numeral 85. The upper ends of the two threaded members 83 and 83a are provided with gear teeth 86 and 87. Both these toothed gears mesh with teeth on a rack 88 extending transversely of the mill and mounted for longitudinal sliding movement. Movement of the rack will produce concurrent movement of the threaded members 83 and 83a.

In FIG. 7 the rack 88 is shown as connected, as by a swiveled coupling, to a shaft 89 threaded into a backet 90 which is fixed on the machine. If the shaft 89 is rotated in either direction there will be a movement of the rack 88 in one longitudinal direction or the other. Changes in the rotative position of the shaft 89 may be effected by any suitable means, automatic or otherwise. For the purposes of an exemplary showing a handwheel has been indicated at 91.

It will be seen that this construction is such that a movement of the rack in either direction will produce an angular adjustment of the upper cage assembly with respect to the lower cage assembly of the mill; and in this way the mill may be adjusted so that opposite working rolls of each pair will engage the working piece simultaneously or predetermined departures from simultaneous operation may be attained.

For adjustment of parallelism of the workingrolls, it is also advisable to provide means for the relative adjustment of the rings at each end of each backing roll. One way of doing this is also illustrated in FIG. 7. Here the gears 63 and 69 are splined to their respective shafts 61 and 67 in such a way as to permit axial movement. Each of these gears is also rotatably coupled to a threaded member 92 or 93, which members are respectively threaded into xed brackets 94 and 95. The threaded members may be rotated by any suitable means (not shown) and in FIG. 7 they have been indicated as provided with lock nuts 96 and 97.

If the gear teeth on rings 57, 58 and 59, 60 together with the gear teeth on the gears or pinions on shafts 61 and 67 are of helical configuration, it will be evident that an axial movement of gear 63 on shaft 61 will adjust the rotative positions of rings 57 and 58 as respects each other, thus correcting or producing skew in the working rolls 4. A longitudinal adjustment of the position of gear 69 will produce a similar adjustment in the relative positions of rings 59 and 60. These adjustments may be made either before, after, or during the operation of the mill. If the rings and gears have straight teeth, the same effect may be obtained by providing helical splines on the shafts 61 and 67.

It has hitherto been pointed out that the occurrence of any form of asynchronism in the mill during rolling is likely to produce effects which are not only cumulative and progressively worsening rapidly but also violent. The means herein described in connection with FIG. 7 provide adjustment means which can be actuated during the rolling operation to correct conditions found by the operator before serious damage to the mill itself. While the last shownV adjustment would not permit of rapid adjustment, it is understood that in the actual mill it is power operated.

FIG. 10 sho-ws another embodiment of means for the adjustment of synchronisrn in mills having rings on cages which are mounted for free relative rotation on backing rolls. The geared portions of the cages of a single backing roll are indicated at 98 and 99. These ring elements spaans/a 1 are connected by pinions ft and 101 respectively to different prime movers such as variable speed electric motors 102 and 103 through the intermediary of gear reduction means 104 and 105. It is advantageous to include iiy wheels 106 and 107 in the system for smooth operation. The left hand system is provided with a Selsyn generator 1(18 which is wired to a Selsyn motor 109 forming part of the right hand system. The right hand system is shown as including a differential 11). The differential has a so-called free member 111 to which an indicating pointer may be attached. So long as the pinions 160 and 101 rotate at an identical speed the pointer attached to differential member 111 will not move. If, however, there should be a speed discrepancy producing as much as one minute of deviation of the angular' positions of pinions 10) and 161 from each other, that discrepancy will manifest itself in a deviation of the pointer attached tothe differential at the point 111.

This fact may be used in several ways. Deviation of the pointer may be caused to generate a signal which will vary the speed of motor 104 so as to restore a predetermined condition of synchronism. Again, a pointer attached to the shaft 111 of the differential may be made se'ttable by the mill operator to various positions so as to establish a new position of angular relationship between pinions 11N) and 101 and the cages or rings which they drive. Alternately an electrical differential indicator may be substituted.

It has been found that relatively small variable speed motors, such as D.C. motors, can be used to obtain synchronization of relatively large mill cages providing they are coupled with suitable y wheels. Forces responsible for throwing planetary rolls out of synchronization are, for the most part, in the form of small sharp shocks which the energy stored in an adjacent flywheel can overcome, whereas, a heavier motor without iiywheel causes torsional elastic deflections because of the unavoidable length of the driving shafts. Similar controls may be applied to the cages or rings of the other backing roll, and adjustments in speed made as between the cages of the two rolls. In this way corrections may be made both for any skewing of the working rolls and for the simultaneous contacting of the opposite sides of the work piece by the working rolls of any given pair.

There is shown in FIGS. 3, 4 and 8 and 9, a type of planetary mill of somewhat different character. In the heavy duty reduction of slabs, it has heretofore been found necessary to drive the backing rolls so that they will in turn frictionally drive the working rolls in the reduction zone of the mill. Attempts to drive the mill by driving the working roll cages while supplying backing through freely rotatable sleeves mounted on driven support shafts have not been found successful because, since the drive is applied only to the necks of the working rolls, these rolls may be broken or subjected to undue strains, or they must be made larger than is desirable in mills of this type. It is known that a small working roll will produce a greater reduction in the work piece under the same mill pressure.

In the figures to which reference has been made, each backing device consists of a shaft 112 or 113 upon which a backing sleeve 114 or 115 is freely rotatable. As shown most clearly in FIG. 4, the working roll retaining rings 116 and 117 are fixed on the shaft 112 while the rings 11S and 119 are fixed on the shaft 113. The shafts, therefore, impart a driving force to the rings but not to the sleeves 114 and 115; which are drivenfrictionally by the working rolls. The difficulties above outlined are overcome by the provision of means for urging a number of the working rolls on opposite sides of the roll bite against the backing rolls, such as arcuate shoe members 120 and 121 on the sides of the planetary assemblies opposite the zone of plastic deformation. These shoes may be lined as at 122 and 123 with a hard substance or a wear resistant material such as plastic to reduce roll wear.

The shoes are strongly urged toward the working roll assemblies 4 and 5. This may be done in various ways. In FIG. 4 each of the shoes is mounted on each end on a bell crank 124 or 125. The intermediate pivots of these bell cranks are on brackets 126 and 127 mounted on the mill frame. The other ends of the bell cranks are connected to the piston rods 128 and 129 of a fluid pressure cylinder 130 containing two pistons in spaced relationship. A similar arrangement, given like index numerals, is shown for controlling the lower shoe 121. It will be obvious that the cylinders 130 can be operated to move the shoes under force against the planetary roll assemblies or to move them in the opposite direction; and it will also be clear that the arrangement may be such as to 'cause the shoes to follow any screwdown movements of the planetary assemblies while continuing to exert the desired degree of pressure on the working rolls.

The result of the operation of the shoes is to press a number of the Working rolls against the backing sleeves 114 and 115 on the side opposite the zone of plastic deformation. The working rolls are being driven through their respective cages, and irrespective of the presence or absence of a work piece in the mill, the working rolls so pressed by the shoes against the backing sleeves will drive the backing sleeves through friction. But because the backing sleeves are so driven, they transmit that drive by friction to such working rolls as may be located in the actual zone of plastic deformation during a rolling operation. Thus, the working rolls which are engaged in the actual reduction of the piece are not being driven solely by the rings at their necks, but are actually being driven frictionally in substantially the same way as they would be driven in the zone of plastic deformation by the solid, driven backing rolls of embodiments of the mill such as are shown in FIGS. l and 2 of this application.

The shoes may be configured to press a relatively large number of the working rolls against their respective backing sleeves; and it will be evident also that two or more shoes may be employed with respect to any given planetary assembly. In many instances, in order to compensate for wear, it will be found advisable to mount the chocks for the working rolls in the rings or cages in such fashion that they may be displaced inwardly radially against resilient means. Thus the majority of the effective drive on the Working rolls which are actually in the zone of plastic deformation will be supplied by friction from the backing sleeve over the entire line of contact between these working rolls and the backing sleeve.

It may be noted that the shoe arrangement just described reduces the load on the main chocks or bearings of the planetary assembly and tends to prevent deflection of the planetary assembly. By the same token, it also effectively reduces vibration in the mill caused by rapid fluctuations of the roll separating force with the passage of each pair of work rolls. This effect is of importance because the actuation of adjusting means as herein described becomes much smoother. There will be found less tendency toward over-correction and consequent shock; and the operation of the adjusting means, especially in producing strip free of back tins on both sides, is made more certain.

In mills where conventional rectangular backing roll chocks are used, a similar effect so far as the damping of vibrations and the enhancement of the response of the mill to means for adjusting synchronization may be obtained by a method of roll balancing which is shown in FIG. 4a. Here a backing roll 131 is shown as having its neck mounted in a chock 132 by means of a main bearing 133. A second bearing 134 is provided as a balancing bearing and is also mounted on the neck of the backing roll and with a separate retaining ring 135. A bolt 136 is connected to the ring and extends upwardly through a portion of the chock, where it is actuated by a spring 137, the force of the spring being greater than the weight of the backing roll 131 and the planetary assembly carried by it.

By such a means, the main bearing 133 may be kept always under load irrespective of the magnitude of the roll separating forces, which is a function of the angular position of a pair or pairs of working rolls in engagement with the work piece.

FIG. 9 shows an exemplary embodiment of a planetary assembly as shown diagrammatically in FIG. 4, i.e. where the work roll carrying cages 116 and 117 are keyed onto the backing shaft 112. Instead of straight keys, said carrying shaft 112 has splined portions 112a and 112b, which engage in corresponding splines provided in the bores of said cages 116 and 117. The shaft 112 is journalled on two cylindrical roller bearings 112C and 112d, provided in eccentric chocks 4b and 4c. As can be seen, these bearings allow the shaft 112 an axial freedom; and its axial position is controlled by the thrust bearing 141 the inner race of which is firmly attached to the .neck of the shaft 112 and moves together with it as one embodiment. The outer races of the bearing 141 are mounted within a collar 158 provided with an external thread. The thread engages with the internal thread of a nut 159 bolted onto the main chock 4c. A gear 169, keyed on the collar 158, engages a pinion 161 which allows for an axial travel of the gear 160.

It will be clear that by turning the pinion 161 either by a hand-operated crank or by any suitable means, the axial position of the backing shaft 112 can be controlled. When moving the shaft 112 to the right it will cause a slight rotation of the two roll carrying cages with respect to said shaft 112, cage 116 turning anti-clockwise and cage 117 clockwise, when observed endwise from the righthand side of the drawing. And vice versa, an adjustment of the axial position of shaft 112 to the left, produces an opposite rotation of the two cages 116 and 117. This in turn influences the parallelism of all the working rolls of the corresponding assembly.

It will be noted that such adjustment and control of the axial position can be made irrespective of whether the mill is stationary or operating.

Referring to FIG. 9, a particular arrangement for mounting the elements of a planetary mill in rotary chocks in a housing is detailed. The shaft 112 has necks 138 and 138a carrying sleeves 139 and 139a. The ring elements 116 and 117 are as above described. The shaft is shown as having a driving coupling 140. The sleeves 139 and 139a are mounted by means of roller bearings 112e and 11261 in the chocks 4b and 4c which in turn are rotatably mounted in the housing elements 1a and 1, and retained therein by the retaining ring 163. The sleeve-114 is rotatably mounted on the shaft 112 by anti-friction means 142 or in any other suitable fashion. Various oil sealing elements are indicated in the drawing but need not be specifically outlined here. These permit the delivery of lubricant to the roller bearing 162 and the withdrawal of lubricant therefrom without giving rise to leakage of the lubricant beyond the bearing area where it might cause the working rolls to skid upon sleeve 114.

FIGS. 6 and 9 show the adjustment means for synchronization and parallelism, respectively, when applied to the type of planetary roll mounting where the working roll cages 117 are keyed into a backing shaft 112 (as shown in FIGS. 3, 4 and 8) and where the backing rolls 114 are mounted on separate bearings 142 on the same backing shaft. In many cases precision keys or splines are adequate to keep working rolls 5 strictly parallel to each other, but especially in mills producing wide width strips the operation is greatly facilitated if the operator has at his disposal, quickly responsive and precise means for adjustment of roll parallelism, and even, as above explained, throwing the rolls very slightly out of synchronism on purpose.

Adjustments which insure the simultaneous Contact of opposite ones of a pair of working rolls with the piece or predetermined departures therefrom are easily attained even while the mill is operating, as shown in FIG. 6K. Here a pair of backing shafts 112 and 113, which for convenience are shown close together in the housing 1, are connected by couplings 143 and 144 to spindles 145 and 146 which in turn are connected by couplings 147 and 148 to the shafts 149 and 159 of a pinion stand 151. Within this pinion stand the shafts are connected together by pinions 152 and 153. A motor or other prime mover may be connected to the projecting end 154 of the shaft 154i. In the particular embodiment the pinions have helical teeth and the pinion 153 is made substantially wider than the pinion 152. The last mentioned pinion is splined to the shaft 149 in such a way that it may move longitudinally thereof. A member 155 is threaded into the casing of the pinion stand and has at one end a shoulder which will x the position of pinion 152, the pinion being urged against the shoulder by spring or other suitable means 156. The member 155 may be adjusted in any suitable fashion as by a Wrench. It is shown as having a lock nut 157. However, it is possible to motorize the member 155 in such a way that adjustments in its position can be effected by the operator from a distance. It will be understood that a longitudinal movement of the pinion 152 will vary slightly the relative rotative positions of backing shafts 112 and 113 so that working rolls mounted in rings afxed to those shafts can be varied or adjusted as to synchronism.

As has been indicated, prior to this invention whenever a planetary mill began to show signs of operating erratically, the operator had no choice but to endeavor to stop the mill before serious damage occurred. In this application various control features have been described which enable the operator to correct for erratic behavior so as to continue the rolling operation, and a method has been described of operating the mill, in such a way as to promptly correct such symptoms before any serious disturbance of the synchronization mechanism and damage has had a chance to occur. It will be evident that the control means herein taught may be modied as to their physical embodiments without departing from the spirit of the invention.

The invention having been described in certain exemplary embodiments, what is claimed as new and desired to be secured by Letters Patent is:

1. A method of operating a planetary mill having feeding means and planetary assemblies comprising each a series of working rolls operating around backing means, there being a planetary assembly on each side of a work piece passing through said mill, comprising the steps of effecting screwdown in said mill by moving said planetary assemblies toward and away from each other by substantially equal and opposite movements whereby to maintain the central plane of said work piece in a substantially constant position despite changes in screwdown, and moving said planetary assemblies in the same direction so as to maintain the screwdown while shifting the plane of symmetry of the mill as determined by the positions of said planetary assemblies.

2. A method of operating a planetary mill having feeding means and planetary assemblies comprising each a series of working rolls operating around backing means, there being a planetary assembly on each side of a work piece passing through said mill, comprising the steps of causing opposite ones of said working rolls to engage the said work piece substantially simultaneously whereby to maintain substantial synchronism, and controlling the behavior of said work piece in a Zone of plastic deformation located between said planetary assemblies and the direction in which the reduced material tends to depart from said zone of plastic deformation, by varying the extent of the departure of said opposite ones of said working rolls from precise synchronism.

3. A method of operating a planetary mill having feeding means and planetary assemblies comprising each a series of working rolls operating around backing means, there being a planetary assembly on each side of a work piece passing through said mill, comprising the steps of maintaining the axes of said working rolls in substantial parallelism with the axes of said backing means, and compensating for variations in the direction in which said work piece tends to leave the zone of plastic deformation located between said planetary assemblies, where said variations in direction occur in the plane of the breadth of said work piece, by producing controlled variations from parallelism between the axes of said working rolls and the axes of said backing means.

4. The process claimed in claim 3 including the further steps of causing opposite ones of said working rolls to engage the work piece substantially simultaneously whereby to maintain synchronism, and controlling the behavior of the said work piece in the said Zone of plastic deformation and the direction in which the reduced material tends to leave the said zone in a plane perpendicular to the first mentioned plane, by producing controlled departures of said working rolls from absolute synchronisrn.

5. In a planetary rolling mill having housing members, a pair of planetary assemblies each comprising working rolls following orbital paths about backing rolls, said assemblies being supported by the engagement of neck members of said backing rolls in bearings in said housing members, the combination of circular chocks for each of said bearings mounted rotatively in said housing members, the said bearings being located eccentrically in said chocks, and means for rotating said chocks in said housing members such that said planetary assemblies will have equal and simultaneous movement in the same direction whereby to shift the plane of symmetry of said mill as determined by the positions of said planetary assemblies.

6. The structure claimed in claim 5 including means for rotating said chocks so as to cause said planetary assemblies to move toward and away from each other, whereby to effect screwdown.

7. The structure claimed in claim 6 wherein actuating means for said chocks comprise each a fluid pressure cylinder and piston, together with means for supplying fluid pressure to each side of said piston, and means for automatically varying the ratio of the fluid pressures on each side of said piston responsively to Variations of the roll separating forces encountered by said planetary assemblies.

8. The structure claimed in claim 6 wherein actuating means for said chocks comprise each a iluid pressure cylinder and piston, together with means for supplying uid pressure to each side of said piston, and means for automatically varying the ratio of the fluid pressures on each side of said piston responsively to variations of the roll separating forces encountered by said planetary assemblies, said means comprising an electrically operated servo valve connected with said cylinder, a potentiometer arranged to be actuated by the piston of said cylinder, said potentiometer being coupled with a second and manually adjustable potentiometer to form a Wheatstone bridge, a source of electrical current for said Wheatstone bridge, means for amplifying an electrical signal derived from said Wheatstone bridge due to imbalance therein, and means for applying said arnplified signal to said servo valve.

9. The structure claimed in claim 6 including a pair of driven pinch rolls for feeding purposes, end portions of said pinch rolls being journalled eccentn'cally in rotary chocks in the same housing members, and means for rotating said last mentioned chocks to effect the pressure exerted on a work piece by said pinch rolls and to shift the plane of symmetry of said work piece with respect to the plane of symmetry of said mill as determined by the positions of said planetary assemblies.

10. The structure claimed in claim 6 including a pair of driven pinch rolls for feeding purposes, end portions of said pinch rolls being journalled eccentrically in rotary chocks in the same housing members, and means for rotating said last mentioned chocks to effect the pressure exerted on a work piece by said pinch rolls and to shift the plane of symmetry of said work piece with respect to the plane of symmetry of said mill as determined by the positions of said planetary assemblies, said pinch rolls lying to one side of said planetary assemblies, a pair of rolls on the opposite side of said planetary assemblies, said last mentioned rolls having their end portions mounted eccentrically in chocks rotatable in the same housing members, and means for rotating said last mentioned chocks whereby to control the pressure of said rolls exerted on said work piece and to adjust the plane of symmetry of said work piece to the plane of symmetry of said mill as determined by the positions of said planetary assemblies.

11. The structure claimed in claim 6 wherein said housing members are tied together across said mill by means of beams, the said housing members and beams constituting a single unitary metal casting.

12. The structure claimed in claim 6 wherein said working rolls of the planetary assemblies are mounted at their ends in rings, and including means for adjusting the rotative positions of the rings for each planetary assembly as respects each other whereby to control a skewing of the axes of the working rolls with respect to the axis of the backing means.

13. The structure claimed in claim 6 wherein said working rolls of the planetary assemblies are mounted at their ends in rings, and including means for adjusting the rotative positions of the rings for each planetary assembly as respects each other whereby to control a skewing of the axes of the working rolls With respect to the axis of the backing means, and means for adjusting the rotative positions of the rings of one planetary assembiy as respects the rings of the other planetary assembly whereby to control the concurrent engagement of opposite working rolls of the two planetary assemblies with a work piece being rolled therein.

14. In a planetary rolling mill, housing means, backing rolls journalled with respect to said housing means, working rolls orbitally related to each of said backing rolls, the working rolls for each backing roll being mounted at their ends in rings rotatable with respect to the backing roll, said rings bearing gear teeth, and adjustable means for tying together the rings of the said backing roll, said means comprising a shaft extending substantially parallel to the axis of said backing roll, and pinions on said shaft meshing with the gear teeth of said rings, one of said pinions being adjustable axially of said shaft on splines, the gear teeth of said pinions and rings being helical, so that the axial movement of said last mentioned pinion will adjust the relative rotative positions of said rings.

15. The structure claimed in claim 14 including a pair of shafts extending between the first mentioned shafts and geared thereto by bevel gears, and means in connection with the last mentioned shafts to adjust the relative rotative positions of the rings of one planetary assembly with respect to the rings of the other planetary assembly.

16. The structure claimed in claim 15 wherein said last mentioned means includes sleeves joining divided portions of said last mentioned shafts, the said shaft portions having splined connections with said sleeve, one at least of said splined connections comprising splines having a helical configuration, and means for adjusting the positions of said sleeves longitudinally of said divided shafts.

17. In a planetary mill, a planetary assembly comprising a backing roll and working rolls traveling as satellites about said backing roll, end portions of said working rolls being mounted in rings rotatively journalled on said backing roll at the ends of said working surfaces thereof,

and driving means for each of said rings, each 0f said driving means comprising a motor, a iy wheel, means including gear reduction mechanism connecting said motor with its respective ring, one of said driving means including a Selsyn generator and the other a Selsyn motor and an electrical connection between said Selsyn generator and Selsyn motor to maintain equal rotative speeds in said rings.

18. The structure claimed in claim 17 wherein one of said driving means includes a differential mechanism having means for indicating any disparity in the rotative positions and speeds of said rings.

19. The structure claimed in claim 18 wherein said differential also includes settable means for producing changes in the relative rotative positions and speeds of said rings.

20. In a planetary mill having a housing, planetary assemblies journalled in said housing and pinch rolls also journalled in said housing, means in connection with said planetary assemblies operative to adjust the position of 20 21. The structure claimed in claim 20 including means for adjusting the positions of the Working rolls in each planetary assembly as respects opposite working rolls in the other planetary assembly to vary the simultaneous engagement of opposite pairs of said working rolls with said work piece.

22. The structure claimed in claim 20 including means for adjusting the positions of the working rolls in each planetary assembly as respects opposite working rolls in the other planetary assembly to control the simultaneous engagement of opposite pairs of said working rolls with said Work piece, and means for varying the axial alignment of the working rolls in each planetary assembly with respect to the axis of the backing roll of such planetary assembly.

Reierenees Cited in the iile of this patent UNITED STATES PATENTS 285,567 Carter Sept. 25, 1883 844,350 Hale Feb. 19, 1907 1,622,744 Stiefel Mar. 29, 1927 2,680,978 Hessenberg lune 15, 1954 2,710,550 Sendzimir June 14, 1955 2,774,263 Leufven Dec. 18, 1956 FOREIGN PATENTS 143.217 Australia Sept. 5, 1951 

1. A METHOD OF OPERATING A PLANETARY MILL HAVING FEEDING MEANS AND PLANETARY ASSEMBLIES COMPRISING EACH A SERIES OF WORKING ROLLS OPERATING AROUND BACKING MEANS, THERE BEING A PLANETARY ASSEMBLY ON EACH SIDE OF A WORK PIECE PASSING THROUGH SAID MILL, COMPRISING THE STEPS OF EFFECTING SCREWDOWN IN SAID MILL BY MOVING SAID PLANETARY ASSEMBLIES TOWARD AND AWAY FROM EACH OTHER BY SUBSTANTIALLY EQUAL AND OPPOSITE MOVEMENTS WHEREBY TO MAINTAIN THE CENTRAL PLANE OF SAID WORK PIECE IN A SUBSTANTIALLY CONSTANT POSITION DESPITE CHANGES IN SCREWDOWN, AND MOVING SAID PLANETARY ASSEMBLIES IN THE SAME DIRECTION SO AS TO MAINTAIN THE SCREWDOWN WHILE SHIFTING THE PLANE OF SYMMETRY OF THE MILL AS DETERMINED BY THE POSITIONS OF SAID PLANETARY ASSEMBLIES. 